# Knowing when to descend

When I’m in a flight I descend to late then I’m always 17 feet above the airport. So I need a bit of guidance of knowing when to descend.

If you multiply your altitude times 3 then that is a good amount. That is if you go down at -2000 FPM ish.

For Example: I am cruising at FL350. 35x3=105. Therefore, you would descend there. What I like to do is start earlier. for FL350 I would start at around 130nm out. It obviously varies if you are going to an airport that is high in Altitude.

High Altitude Example: DEN is at an altitude of 5430 ft. I would round it down to 5400. So if you are cruising at FL350 you would subtract 5400 then multiply by 3. 35,000-5400= 29,600. Then 29x3=87nm. I would descent at around 100nm at around -1,500 to -1,800 FPM.

Hope this helps!

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Try using IF Flight Plan Converter in conjunction with a planning tool like Simbrief. This will give you some good guidance as to what altitude and speed you need to be at a given fix and when to start your descent and the respective fpm calculation

You can always enter a hold to shed off some altitude and make your approach all that more easier

Just remember that if you are instructed by ATC to descend to a flight level you should follow this regardless of what flightplan you have filed

You can also look up the approach (STAR) and departure (SID) charts for your chosen airport to see what the altitude restraints are as terrain will obviously become a factor, especially at airports like Innsbruck

I used to multiply my altitude in thousands by 3 but I always found out I was a bit too high so I ended up dividing my flight level by 3

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I usually fly at FL320 cruising altitude. When the distance to my destination is about 150-125NM, I start my descent at a rate of 1500 FPM. I gradually slow down my speed to 0.68M (+/- 250 knots).

When I’m nearing 50NM, I make sure I’m around FL150 and continue my descent at the same rate and the same speed down to 4000 FT all the way to the runway’s localizer.

When I have the impression I’m flying too fast, I slow down up to 230-200 knots.

This method works for airports at an altitude of 0 ft and no hills or mountains along the glide slope. I’m still learning how to adapt this method at different airports.

Here is how I do it and it maybe rough.
7,500-15,000 ft 30-50 nm
15,000-25,000 ft 50-80 nm
25,000-35,000 ft 80-120 nm
35,000-40,000 ft 120-150 nm
VS ranges from initial descent 800 fpm to descent no more than 2,200 fpm.
When you are with 50 nm of the airport be between 14,000-16,000 feet.
This is my method of descending with a 100% success rate.

Well, the way I do it is easy and effective but easy to remember also. Basically, if i’m cruising at FL350 and i’m trying to get down to the airport all I do is take 100 and add the first 2 numbers of my elevation. In this case 100 plus 35 (for 35,000ft), and I will need to descend 135nm away from the airport, assuming it is less then 1,000ft in elevation. if the Airport is 1,000ft in elevation or more, all you do is subtract how many feet it is high from your number. Say the airport is 2,500 feet in elevation and I’m cruising at FL350, I would take 135 and subtract 2 (for the first number from airport elevation). leaving me with a descent distance of 133nm out. Hope this help! if you have any questions about this method I’m here!

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The other manner to calculate the TOD is apply the rule of 3. It is most easy and can check the descent for parts.
Example:
We are at FL 300 and we want to descend to 8000ft because is our IAF (initial approach fix) easy.

Current altitude= 30000
IAF =8000
Nm to descend=?
V/s = ?

30000-8000= 22000ft firt step
22000/1000= 22
22x3=66nm
Add 10 nm for variations of wind and v/s
TOD= 76 nm

To calculate the V/s
We take 250 kts our ground speed add a 0 will be 2500 and divided x 2
250+0=2500
2500/2=1250ft/min
V/s=1250ft/min

Obviously it is only for constant descent
You can fix any variation checking descent for leg

Example:
76nm of IAF We’ll be at Fl300
56nm of IAF We’ll be at Fl200 etc…

Keep on mind that any part of flight need a briefing before performing. Thanks

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Since I’m lazy
My way of doing it is really a rough estimate with barely any math
Subtract the my cruise by the airports elevation
FL280-340[100-119nm]
FL350-400[120-140nm]
I always have no problems but it’s probably me finding the perfect distance from the airport to decend at any altitude

My way of doing it was given to me by @Ethan_Chloe123, but I’ve edited it slightly. Here’s the formula :
[(Cruise Altitude (just the first 2 numbers) - 11/12 (11
If you’re going east, 12 if you’re going west) + altitude of airport rounded to the nearest thousand, just the first number (or 2) (if it is less than 1000ft, do not worry about this part)) x3] + 50nm + 12 for potential winds.
For example : If your cruise altitude was FL330, and you were heading west, and the altitude of your destination airport was 2000ft, here is what you would do :
[(33 - 12 + 2) x 3] + 50 + 12
[(11 + 2) x 3] + 62
[13 x 3] + 62
69 + 62
131 nm out is when you would start descent at -2000 or -2500 fpm until 12,000MSL, slow to 240, then at 50nm out -1500 until 5000, slow to 200, then at 25nm out -1000 until 3000 and intercept localizer.
I know it seems difficult but once you get the hang of it, it’s pretty simple, and it works excellent every time!

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I use a simple rule (not extremely accurate…):

1. Get the amount of feet you need to descend. (If you’re at FL350 and your destination airport is 1000ft MSL, your number would be 35000)

2. Take the last 3 zeroes off of the number:
35000 —> 35

3. Multiply that by 3.
35 * 3 = 105
TOD = 105nm

4. Take your groundspeed (ex. 450kts)
Multiply that by 5.
450 * 5 = 2250

2250fpm is your initial descent speed.

Since your groundspeed keeps changing as you descend, you’ll need to do your FPM calculation multiple times until you get to the airport. (I do it roughly every 20kts of change on the groundspeed.)

Credits to @TheDeltaFlyerr for showing me this rule a looong time ago.

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